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Stock-Based Compensation - Total Gross Unrecognized Estimated Compensation Expense and Expected Weighted-Average Periods (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Unrecognized estimated compensation expense for nonvested awards $ 26,800us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Stock Options [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Unrecognized estimated compensation expense for nonvested awards 1,457us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Weighted-average period for expense recognition 1 year 1 month 6 days
Restricted Stock and Restricted Stock units [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Unrecognized estimated compensation expense for nonvested awards 21,164us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= mdr_RestrictedStockUnitsAndRestrictedStockMember
Weighted-average period for expense recognition 2 years 1 month 6 days
Performance Shares [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Unrecognized estimated compensation expense for nonvested awards $ 4,140us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Weighted-average period for expense recognition 1 year 10 months 24 days